One option is to install LiveUpdate Administrator 2.x (LUA 2.x) on a server that does have access to the Internet, and configure it to supply content at a Distribution Center (DC) that the SEPM can access. Configure the Symantec Endpoint Protection Manager to retrieve updates from this Distibution Center. See the following documents for more information:

Installing and configuring LiveUpdate Administrator 2.x

How to configure LiveUpdate to use alternate sources through the Symantec Endpoint Protection Manager Console

An alternative option for updating Antivirus and Antispyware definitions only are explained in the following document:

How to update definitions for Symantec Endpoint Protection Manager using the .jdb file
 

Without using Liveupdate Administrator 2.x, there currently is no way to update the Proactive Threat Protection (PTP) and Network Threat Protection (NTP) definitions on the Endpoint Protection Manager.

Please note that, without direct Internet access, some features of the SEPM will not be able to function. One example is the Security Response box on the SEPM interface.



Technical Information
The two methods described in this article (LUA 2.x and via .jdb or Intelligent Updater manually copied on removable media) will also successfully update individual SEP clients on an isolated network. If unmanaged SEP clients are to be used with LUA 2.x, be sure to update client settings via the exported Settings.Hosts.LiveUpdate file so that the SEP clients will be able to communciate and retrieve materials from the LUA server.